Molybdenum coated article and method of making



y 1954 c. G. GOETZEL 2,683,305

MOLYBDENUM COATED ARTIQLE AND METHOD OF MAKING Filed July 15, 1949INVENTOR. A2 41/5 5 501-7254 Wyzw/ HTTDR'NEYS Patented July 13, 1954UNITED STATES PATENT OFFICE MOLYBDENUM COATED ARTICLE AND METHOD OFMAKING Application July 15, 1949, Serial No. 105,035

6 Claims. 1

This invention relates to protective surfaces for structural componentsuseful under high temperature and corrosive atmosphere conditions andparticularly to protective surfaces or casings for the refractory metalmolybdenum, the protective surface casings being integrally fused anddiffused with the base substance.

Components suitable for use as buckets, blades, valves, nozzles, and thelike, in gas or steam turbines, jet engines and devices having similartemperature and atmosphere conditions present problems difficult tosolve. Such components must have certain desirable physicalcharacteristics so that they will withstand the stresses involved andyet will not deteriorate under oxidizing or corrosive conditions. Theelements must have high hot tensile strength, hot fatigue strength, andhigh resistance to creep at elevated temperatures.

Molybdenum possesses certain desirable characteristics which make itadaptable for structural materials exposed to high temperatures.Molybdenum in contrast to some other of the refractory metals is notvery much heavier than certain of the alloy steels, nickel base alloysor cobalt base alloys, the specific gravity of molybdenum being 11.2.Because of its high fusion and evaporation temperatures, molybdenum hasa very high modulus of elasticity which is in the order of 50,000,000

pounds per square inch. This indicates a high resistance to deformationand creep at very high temperatures. Also, the strength of molybdenum ishigh, particularly if in the wrought condition. For wire and sheetmaterials, a tensile strength of 90,000 pounds per square inch at 1100F., and

37,000 pounds per square inch at 2000" F. is attainable. V In order toutilize these desirable physical properties, it is necessary to preservethe fine grain structure of the highly worked molybdenum metal. It alsois important in subsequent treatments applied to the metal, not tooverheat beyond about 2200 F., because in high purity molybdenum, suchwill cause excessive recrystallization and grain growth.

Molybdenum is abundantly found in the United States and its miningprocesses, metallurgy, physical metallurgy and metal working practiceshave been perfected. Further, the production of molybdenum products bypowder metallurgy techniques, and also lately by casting techniques, hasbeen perfected so that large ingots and shapes up to 250 pounds andsizes up to 7" in diameter and30" in length can now be produced.

One of the biggest difliculties has been that molybdenum is increasinglysusceptible to oxidation at temperatures above 1100 F. This is becausethe reaction of molybdenum with oxygen results in the formation ofmolybdenum trioxide which becomes highly volatile at temperatures above1650" F. Because of this, when the metal is exposed to temperatures of1650 F. and higher, a rapid thermal decomposition will take place andthe metal will be destroyed by the attack of oxygen. The attack willprogress from the periphery to the core of the exposed body.

Because of this problem, it has been recognized that unless a protectiveatmosphere or vacuum is provided, such as in incandescent lamps or X-raytubes, access of oxygen to the surface of the molybdenum must beprevented by employing physical or physico-chemical means which willpermit retention of the metallic structure of molybdenum up to thetemperature limits set by the aforementioned recrystallization and graingrowth.

Surface protection has been attempted by conventional means such as byenveloping the metal in a stable ceramic, such as Silimanite or alumina,in the form of shells, tubes, etc. Spraying of the ceramic material inthe form of a slurry and subsequently baking also was tried as well asslip-casting various washes of ceramic compositions differing in thermalexpansivity and cementing properties. Other physical processes have beentried such as the surface deposition of metallic, semi-metallic ormetalloidal substances onto molybdenum by such chemical treatments asprecipitation or reaction displacement methods from suitable salts,these processes being carried out at ordinary temperatures or elevatedtemperatures. Electro-deposition, deposition from the vapor phase, orthermal decomposition from certain compounds also have beentried. In thecoating processes just mentioned, the surfacing or casing did notachieve lasting results.

Molybdenum metal regardless of its comparatively large atomic radius andhigh heat of reaction due to its high melting point has a highcoefiicient of diffusion at elevated temperatures and molybdenum forthis reason penetrates at an increasingly rapid rate with risingtemperature into other high melting metals as well as into alloys orcompounds. Stable compounds such as the refractory oxides A1202, S102 orMgO when brought into contact with molybdenum metal at high temperaturesare penetrated by the molybdenum. It can be theorized that placeexchange reactions occur so that the molybdenum atoms switch positionswith aluminum, silicon, or magnesium in the compounds and that complexcompounds of the type containing the elements molybdenum and/ormolybdenum oxide comsilicon, oxygen; or molybdenum, magnesium, oxygenare formed. There is a possibility that molybdenum atoms migrate througha grain boundary until they reach exposed surfaces. It also is possiblethat the stable oxides are locally reduced by the molybdenum and thatthe resulting molybdenum trioxide because of its very high vaporpressure penetrates through the crystal structure or the boundaryregions of the stable compound. In any event, the penetration of themolybdenum and/or molybdenum oxide, compounds result in exposure toerosion and corrosion of the protective stable oxide surfaces.

One of the objects of this invention is the protection of molybdenum byutilizing a surfacing or casing method which provides for the protection(physically, chemically and metallurgically) of the molybdenum basemetal, said surfacing or casing method also protecting the molybdenumagainst deterioration.

In one aspect of the invention, intermediary layers are placed betweenthe molybdenum base and the corrosion resistant surface casing. Theproper selection of the intermediate layer will enable formation ofintermetallic compounds with the molybdenum, these compoundsconstituting the necessary barriers respective to diff-tbsion of themolybdenum into the surface casing and the surface metal into themolybdenum base. This is based on the fundamental difiusion laws whichhold that diffusion rates are retarded inthe presence of compounds sothat migration of the molybdenum through a barrier of molybdenumcontaining intermeta'llic compounds will be slowed down. If, however,the compound functioning as a diffusion barrier is not of theintermetallic type, such as the system molybdenumiron ormolybdenum-nickel, but is of a nonmetallic type, such as a carbide,boride, silicide, etc., either of molybdenum or even better of .aforeign metal or non-metal, outward diffusion of molybdenum will befurther inhibited.

It is a further object of the invention to produce synthetically, anintermediate layer in such a way as to offer one or, if possible,several suecessive continuous layers functioning as moderators orslow-down agents for the migrating molybdenum atoms, thus providing acasing for a molybdenum base metal which will be stable for long periodsof time under high temperature oxidizing atmospheres.

By introducing soft and plastic metal layers,

between the non-metallic compound barrier layers, stress concentrationsdue to differences in expansivity or externally caused stresses, such ascentrifugal forces, dynamic loads, etc, are relieved or eliminated.

These and other objects, advantages and features of the invention willbecome apparent from the following description and drawings.

Figure l diagrammatically illustrates one form of the invention.

Figure 2 diagrammatically illustrates another form of the invention,

Figure 3 illustrates one type of apparatus which may be used for coatinmolybdenum sheet.

Figure 4 represents another type of apparatus which can be used forcoating molybdenum sheet.

Figure 5 is an enlarged view of molybdenum sheet showing one manner inwhich the edges can be covered.

In one form of the invention, an intermediate layer of an iron-nickelalloy containing between 36% and 50% nickel can be used. The nickel,iron, or similar alloy layer can be produced on the molybdenum base invarious manners such as by electro-deposition, spray coating or by thecarbonyl process.

The pure metals iron, nickel, or cobalt; binary alloys of iron andnickel, iron and cobaltor nickel and cobalt; ternary alloys of iron,nickel and eobalt can be electro-deposited in a conventional manner inany desired ratio onto the finished molybdenum body. In case of analloy, the deposit may either be of a homogeneous type, solid solutionsfor most ratios, or it may be deposited in individual successive layersor zones. The 'electro-deposit is then diffused and merged with themolybdenum base part by a subsequent heat treatment under protectiveatmospheres. Due to the comparative stability of electro-deposits,temperatures of a high order and prolonged times are required for thediffusion processes.

The pure metals iron, nickel and cobalt; the binary alloys of iron withnickel, iron with cobalt and nickel with cobalt; and the ternary alloysof iron, nickel and cobalt in any desired proportion can be applied tothe molybdenum base by conventional spray methods. For this purpose, themetal or alloy can be employed in wire form or as an alloyed anddisintegrated powder. Also, the metals can be deposited in indiviluallayers and their diffusion controlled in the subsequent treatment togive the desired concentration :zones for adequate matching oftheir-expansivity with that of the base metal .or the ultimate surfacematerial. Due to the history of such spray coating-s, which in generalemploy slightly oxidizing conditions, an intensive reduction anddillusion treatment is required for perfect bonding and merging of thedeposit with the molybdenum base metal.

The metals iron, nickel and cobalt; the binary alloys between iron andnickel, iron and cobalt, nickel and cobalt; and the ternary alloys ofiron, nickel and cobalt; and also binary, ternary or quaternary alloysof the metals iron, nickel and cobalt, respectively, with. molybdenum,the latter preferably in minor proportion, can be deposited on themolybdenum base by the thermal decomposition of the respective metalcarbonyls. This method, employing the formation of the simple ormultiple carbonyl compounds by the well-known process of combining themetal or alloy in question with carbon monoxide into the liquidcompounds with the aid of high pressure (up to 2000 atms.) and aslightly elevated temperature (about ZOO-400 F), followed by adecomposition of the complex carbonyl compound at a somewhat highertemperature (about 600-800 F.) and ordinary pressures, is particularlysuitable for the purpose of this invention. The deposits obtained, beingeither in form of a powder or of a sponge ones a coherent solid film orlayer depending on the conditions prevailing in the decompositionchamber with the latter type of deposit obtainable whenthe mclyb denumpart is suspended directly in the heat zone of the decompositionchamber, are highly reactive and known .to result in high .rates ofdiffusion at very low temperatures such as in the range of 1200-1650 F.It is this latter fact which is of particular importance, since it enables diffusion bonding of the layer to the molybdenum at a temperaturelevel which is safely below the one at which any significant changes ingrain structure or physical properties could occur.

Thereafter an oxidationlproof and corrosion resistant surface casing canbe placed on top of the intermediary alloy layers which is described.The preferred manner for deposition of the surface metal is by the vaporphase methods involving either pure metal or a compound of metal thattermally decomposes upon deposition, initiating a metal atom exchangeprocess. In the case of pure metals, chromium, silicon, zirconium, oraluminum, are the most desirable. Although pure chromium as surfacingcasing is desirable for reasons of technical simplicity and economy ofthe process, the oxide of chromium (Cr O3) formed when exposing themetal to high temperature oxidizing atmospheres lacks some stabilityfrom a mechanical standpoint, and tends to mechanically disintegrate andflake and spall off, thus, constantly exposing fresh metal surfaces tothe oxidizing atmosphere. This would eventually result in completelywearing through the chromium metal surface. Hence, metals giving morestable oxide films, such as zirconium, silicon, or aluminum arepreferred for very high temperature application (above 2000 F.).

If the case formation process employs the previously mentioned mechanismof preferred decomposition of a compound, the halides of chromium,silicon, zirconium, or aluminum, such as chromous chloride, chromousiodide, silicon chloride, zirconium chloride, or aluminum chloride aresuitable for the process.

Instead of the pure metals, it may be more advantageous and preferred toemploy alloys of chromium with other metals mentioned which tend to formmore stable complex oxides. Examples of alloys of chromium with elementsto form a more stable oxide, are compounds of chromium with aluminum,with silicon, with zirconium, with aluminum and silicon, with aluminumand zirconium, or with aluminum, silicon and zirconium. In either case,double or triple halides, such as the chlorides, bromides or iodides ofchromium plus aluminum, chromium plus silicon, chromium plus zirconium,chromium plus aluminum plus silicon, chromium plus aluminum pluszirconium, or chromium plus aluminum plus silicon plus zirconium, mustthen be employed.

Reference also may be made to applicants copending application, SerialNo. 94,092, filed May 19, 1949 (now U. S. Patent No. 2,612,442), fordetails of the various manners of depositing the surface casing on theintermediate layers. The comparatively high degree of surface activityof the carbonyl type deposit is of great advantage in producing integralbonding, fusion and merger between the surface casing metals, alloys orcompounds on the one hand and the intermediate layer and the base metalon the other. Thus, low temperatures and short times can be used forthedeposition, displacement and atom exchange processes underlying theoxidation proof case formation, which is of great ad-- vantage in viewof the desirability to prevent heating the molybdenum base metal aboveits recrystallization. temperature.

In another aspect of the invention, the molybdenum base metal part canbe carburized and then a soft metal introduced, such as iron, nickel ortheir alloys, by electroplating, spraying or carbonyl vapor deposition.The carburizing will result in a gradient of carbon concentration.Bonding then can be accomplished by appropriate diifusion treatmentprior to application of the stable oxide surface casing. The bondingtreatment subsequent to carburizing can, if necessary, be performed at atemperature above the melting point of the iron, nickel or alloythereof. This will result in impregnating any pores produced during thecarburizing of the molybdenum with the liquid metal or alloy,respectively.

Instead of the formation of carbides, etc., of molybdenum, similarcompounds can be formed from other metals or non-metals, such as ironcarbide or a complex carbide of iron and silicon, or nickel and silicon,or iron and boron, or nickel and boron. Conventional packs for gascarburizing methods can be used advantageously on iron or some of theother metal or alloy layers which have been deposited previously on orbonded with the molybdenum base metal surfaces. The aforementionedcarbonyl vapor process has the advantage of suflicient flexibility toallow the deposition of successive layers of iron, iron carbide, nickeland the like, in any desired sequence and to any desired layer thicknessin one operation. By varying the cycle with regard to temperature andtime, it is possible to deposit a considerable number of alternatelayers of the iron type metal and an alloy rich in iron carbide.

In the case of other barrier compound forming metals to be deposited asintermediate layers, silicon and aluminum are of particular significancesince they are also'constituents of the complex ultimate surface casing,thus, functioning as diffusion and reaction moderators ahead of thereaction process involving the ultimate complex surfacing casing.

Aluminum deposits can be applied, either directly onto the molybdenum,or on an intermediate layer of iron, nickel, or nickel-iron alloy, bydipping the body into the liquid metal, into a suspension in a fusedaluminum halide bath, or by placing into an enclosure in a calorizingpowder pack. Silicon deposits likewise can be produced directly on themolybdenum, or the intermediate iron, nickel, or nickel-iron alloylayer. Pack siliconizing as well as thermal decomposition of siliconhalides are suitable methods for application of silicon deposits. Italso is possible to combine the above cited treatments with theaforementioned carburizing treatment, which is particularly advantageousin the case of siliconcarbon combinations which yield the very stablesilicon carbide compound, a most effective inhibitor to diffusion ofmetals.

As previously mentioned, iron, nickel and ironnickel compounds can bedeposited on the molybdenum base to form an intermediate barrier layer.as described.

Referring to Fig. 1, direct coverage of molybdenum is illustrated, themolybdenum base being indicated at it with a Type 1 layer ii thereon,said layer consisting of carbon, boron, aluminum, silicon, boroncarbide, silicon carbide, and other metals and compounds combined withthe molybdenum into complex compounds. Layer H is placed on themolybdenum in any of the manners previously described. The next layer 2,a Type II layer, may be of iron, nickel, or iron-nickel alloys aspreviously mentioned, of a type to diffuse into the compound of thefirst layer of material H or to alloy with molybdenum. The outer case orsurfacing material it, Type III layer, may be chromium, silicon, oraluminum, or binary or ternary alloys thereof, bonding and conversioninto stable complex oxide compounds being accomplished by diffusiontreatment.

The outer casing is thereafter deposited An indirect coverage ofmolybdenum is seen in Figure. 2 wherein the molybdenum body is indicatedat 1 2 having intermediate layers 15 and I5 (Type II). of iron, nickel,iron-nickel alloys, to diffuse or penetrate layer H or to alloy with themolybdenum. Layer H (Type I) may be carbon, boron, aluminum, silicon,boron carbide, silicon carbide, combined. with the molybdenum to formcomplex compounds. The outer casing I8 (Type III) may be chromium,silicon, aluminum, or binary or ternary alloys thereof.

The various layers may be formed or deposited as follows:

Type I 1. Carburizing:

a. gas carburizing 27. pack carburizi-ng 2. Al'uminizing:

a. liquid metal dip b. halide salt bath immersion c. halide gasdecomposition 3'. Sili'conizing:

a. pack-impregnation b. halide gas decomposition Type II 1. Spraying 2'.Electroplating 3. Carbonyl process Type HI 1. Pack-impregnation 2.Halide gas decomposition 3. Halide salt bath immersion As an example ofone method of surfacing molybdenum sheet with silicon carbide or boroncarbide serving as the intermediate barrier layer against difiusion,reference may be made to Fig. 3 wherein the molybdenum sheet isindicated at Hi. The sheet preferably is shot-blasted in order to obtaina proper anchorage. The sheet is fed past a feed hopper 23 containingthe carbide grains or a mixture of carbide grains and iron or molybdenumpowder. The sheet is passed through a heating furnace 2! having aprotective atmosphere, the temperature of said sheet being raised to1296-1830 F. The sheet is then passed between two carbide rolls 22. Inorder to cover the other side of the sheet, it can be reversed and againpassed through the apparatus.

Another manner in which the carbide can be placed on this sheet isillustrated in Figure. 4. wherein the shot-blasted molybdenum sheet 23,is passed through heating furnace :24, said, furnace being maintainedwith a protective atmosphere therein. Said sheet is heated to atemperature between 1299-1830" F. Spray guns 25 can be located on eitherside of the sheet for spraying hot SiC Or BiC particles with or withoutiron or molybdenum powder admixed as a binder.

Various methods can be used to insure that the edge is properly covered.For example, the strip 28 (Fig. 5) can have the carbide surface 2":formed thereon with upstanding portions 28, 28 which can be rolled overthe edges to cover the same at 29', 28 to completely protect the sidesof the sheet 25. Also, the edges of the sheet could be pointed so thatthe carbide surface would cover substantially the entire sheet faceincluding the sloping face.

An example of one type of surfaced body is one wherein the molybdenumbase is carburized by a gas carburizing proce. M020 being formed. Ironis then deposited on the carburized molybdenum base body by the carbonylprocess and 8'. thereafter a. silicon-chromium. alloy is deposited onthe iron layer by a pack-impregnation process.

Another example of the inventionis one wherein the molybenum base hasiron. depositedthereon by the carbonyl process followed bycarburizationof the iron layer to form FezC. The carburization iscarriedout so that there is' a gradient of carbon concentration. Thereafter,another casing of iron is formedv by the carbonyl. process and asilicon-chromium outer casing integrally merged in a pack-impregnationprocedure,

A third example is one wherein the molyb denum base is aluminized by apack-impregnation deposition procedure. Following this, iron isdeposited thereon by a carbonyl process and the iron carburized. Anotherlayer of iron can be deposited by the carbonyl process, and a.siliconchromium-aluminum outer casing then intogrally merged with thebody by means of a packimpregnation procedure and heat treatment.

A fourth example is one similar to the aforementioned third example withthe exception that a casing of iron is integrally merged with themolybdenum base before deposition of aluminum.

A fifth example is one wherein the molybdenum base is siliconized by apack-impregnation process and then has iron deposited thereon by meansOf a. carbonyl process. Following. this, a siliconchromium casing isdeposited by a. pack-impregnation technique and then integrally mergedtherewith.

A sixth example is one wherein the molybdenum bod has iron depositedthereon by means of the carbonyl process followed by siliconizing bypack-impregnation. Iron is then deposited thereon by the carbonylprocess and thereafter the iron, is carburized by means of packcarburizing. A further coating of iron then is deposited thereon by acarbonyl technique. The outer casing of silicon-chromium then is placedthereon by pack-impregnation and. integrally merged with the body.

As a seventh example, the third example can have the coating of ironreplaced with a. coating of iron-nickel with a nickel content. of36-50%, said iron-nickel being deposited by a carbonyl process.

The eighth example is similar to the aforementioned sixth example,except that an iron-nickel allo is placed directly on the molybdenumbefore deposition of silicon thereon.

Pack-impregnation is. disclosed in applicants aforementioned co-pendingapplication Serial No. 94,092 (now U. S. Patent No. 2,612,442). Ingeneral, pack-impregnationcan be carried out by placing the body in apack composed of the pulverized material involved and passing a halidegas through the pack at the required high temperature. a

It is to be understood that variation may be made in the examples oftechniques without departing from the spirit of the invention except asdefined in theappended claims.

What is claimed is:

i. In a method of inhibiting the volatilization of molybdenum asmolybdenum trioxide resulting from the reaction of a molybdenum-basebody with oxygen-containing atmospheres at elevated temperatures, theimprovement which comprises providing a coating of at least oneintermediate layer of a metal selected from the group consisting ofiron, nickel, cobalt and alloys thereof on the exposed surface of saidmolybdenum-base body, subjecting the thus-coated body. to heating in anon-oxidizing atmosphere at detail in an elevated temperature sufficientto integrally merge said layer to the molybdenum-base body by diffusionso as to form a barrier zone thereon with molybdenum, then surfacingsaid coated molybdenum-base body with at least one protective layer ofmetal selected from the group consisting of chromium, silicon, aluminum,zirconium and alloys thereof and bonding said protective surface layerof metal to said intermediate barrier zone layer by diffusion heattreatment, whereby the intermediate barrier zone substantially inhibitsthe migration of atoms of molybdenum to the surface of the body and ofatoms of the surface metal layer into the molybdenumbase body such thatthe attack of the molybdenum-base body by oxygen-containing atmosphereis greatly inhibited at elevated temperatures of about 1650 F. andhigher. 7

2. In a method of producing components from a molybdenum-base bodyadapted to withstand corrosion at elevated temperatures and suitable forthe production of buckets, blades, valves, nozzles, and the like, in gasturbines, steam turbines, jet engines and other devices employed undercomparable temperature and atmospheric conditions, the steps comprisingproviding a coating of at least one intermediate layer of a metalselected from the group consisting of iron, nickel, cobalt and alloysthereof on the exposed surface of said molybdenum-base body, subjectingthe thus-coated body to heating in a nonoxidizing atmosphere at anelevated temperature of at least about 1200 F. to integrally merge saidlayer by diffusion to the molybdenum-base body so as to form a barrierzone thereon with molybdenum, then surfacing said coated molybdenum-basebody with at least one protective layer of metal selected from the groupconsisting of chromium, silicon, aluminum, zirconium and alloys thereofand bonding said protective surface layer of metal to said intermediatelayer by diffusion heat treatment, whereby the intermediate barrier zonesubstantially inhibits the migration of atoms of molybdenum to thesurface of the body and atoms of the surface metal layer into themolybdenum-base body such that the protectively surfaced molybdenum-basebody has substantially improved resistance to deterioration and tocatastrophic oxidation at elevated temperatures of about 1650 F. andhigher.

3. In a method of producing components from a molybdenum-base bodyadapted to withstand corrosion at elevated temperatures and suitable forthe production of buckets, blades, valves, nozzles, and the like, in gasturbines, steam turbines, jet engines and other devices employed undercomparable temperature and atmospheric conditions, the steps comprisingproviding a coating of at least one intermediate layer of a metalselected from the group consisting of iron, nickel, cobalt and alloysthereof on the exposed surface of said molydenum-base body, subjectingthe thus-coated body to heating in a non-oxidizing atmosphere at anelevated temperature of at least about 1200 F. to integrally merge saidlayer by diffusion to the molydenumbase body so as to form a barrierzone thereon, then surfacing said coated molydenum-base body with aprotective layer of metal selected from the group consisting ofchromium, silicon, aluminum, zirconium and alloys thereof by depositionfrom a vapor phase containing said metal and bonding said protectivesurface layer of metal to said intermediate layer by diffusion heattreatment, whereby the intermediate barrier zone substantially inhibitsthe migration of atoms of molybdenum to the surface of the body andatoms of the surface metal layer into the molydenumbase body such thatthe protectively surfaced molybdenum-base body has substantiallyimproved resistance to deterioration and to catastrophic oxidation atelevated temperatures of about 1650 F. and higher.

4. In a method of producing buckets, blades, valves, nozzles, and thelike, for use in gas turbines, steam turbines, jet engines and otherdevices employed under comparable temperature and atmospheric conditionsfrom a molydenumbase body, the steps comprising forming a gaseous metalcarbonyl phase containing a metal carbonyl selected from the groupconsisting of iron, nickel and cobalt carbonyl and mixtures thereof,bringing said metal carbonyl phase in contact with said molydenum-basebody, decomposing said gaseous metal carbonyl phase at a temperature ofabout 600 F. to 800 F. and depositing a coating of at least oneintermediate layer of a metal selected from the group consisting ofiron, nickel, cobalt and alloys thereof on the exposed surface of saidmolybdenum-base body, subjecting the thus-coated body to heating in anon-oxidizing atmosphere at an elevated temperature of at least about1200 F. to integrally merge said layer by diffusion to themolybdenumbase body so as to form a barrier zone thereon withmolybdenum, then surfacing said coated molybdenum-base body with aprotective layer of metal selected from the group consisting ofchromium, silicon, aluminum, zirconium and alloys thereof and bondingsaid protective surface layer of metal to said intermediate layer bydiffusion heat treatment, whereby the intermediate barrier zonesubstantially inhibits the migration of atoms of molybdenum to thesurface and atoms of the surface metal layer into the molybdenum-basebody such that the protectively surfaced molydenum-base body hassubstantially improved resistance to deterioration and to catastrophicoxidation at elevated temperatures of about 1650 F. and higher.

5. In a method of producing buckets, blades, valves, nozzles, and thelike for use in gas turbines, steam turbines, jet engines and otherdevices employed under comparable temperature and at mosphericconditions from a molybdenum-base body, the steps comprising forming agaseous metal carbonyl phase containing a metal carbonyl selected fromthe group consisting of iron, nickel and cobalt carbonyl and mixturesthereof, bringing said metal carbonyl phase in contact with saidmolybdenum-base body, decomposing said gaseous metal carbonyl phase at atemperature of about 600 F. to 800 F. and depositing a coating of atleast one intermediate layer of a metal selected from the groupconsisting of iron, nickel, cobalt and alloys thereof on the surface ofsaid molybdenum-base body, subjecting the thus-coated body to heating ina non-oxidizing atmosphere at an elevated temperature of about 1200 F.to 1650 F. to integrally merge said layer by diffusion to themolybdenum-base body so as to form a barrier zone thereon withmolybdenum, then surfacing said coated molybdenum-base body with aprotective layer of metal selected from the group consisting ofchromium, silicon, aluminum, zirconium and alloys thereof by depositionfrom a vapor phase containing said metal and bonding said protectivesurface layer of metal to said intermediate layer by diffusion heattreatment, whereby the intermediate barrier zone substantially inhibitsthe migration of atoms of molybdenum to the surface and atoms of thesurface metal layer into the molybdenum-base body such that theprotectively surfaced molybdenum-base body has substantially improvedresistance to deterioration and to catastrophic oxidation at elevatedtemperatures of about 1650 F. and higher.

6. A protectively surfaced molybdenum-base body having substantialresistance to catastrophic oxidation in oxygen-containing atmospheres atelevated temperatures which comprises a molybdenum-base portion, anintermediate layer of a metal selected from the group consisting ofiron, nickel, cobalt and alloys thereof covering the exposed surface ofsaid portion, said intermediate layer being merged integrally with saidmolybdenum-base surface and being characterized by a difiusion barrierzone containing molybdenum, and a surface layer of metal selected fromthe group consisting of chromium, silicon, aluminum, zirconium andalloys thereof covering said inter- 12 mediate layer and mergedtherevuth, whereby said body has improved resistance to oxidation atelevated temperatures of about 1650 F. and higher.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,650,979 Brace Nov. 29, 1927 1,718,563 Kelley June 25, 19291,899,569 Howe Feb. 28, 1933 2,096,924 Schwarzkopf m--- Oct. 26, 19372,109,485 Ihrig Mar. 1, 1938 2,304,297 Anton g Dec. 8, 1942 2,450,851Colbert Oct. 5, 1948 2,450,855 Colbert Oct. 5, 1948 2,450,856 ColbertOct. 5, 1948 2,475,601 Fink July 12, 1949 2,497,090 Miller Feb. 14, 1950

6. A PROTECTIVELY SURFACED MOLYBDENUM-BASE BODY HAVING SUBSTANTIALRESISTANCE TO CATASTROPHIC OXIDATION IN OXYGEN-CONTAINING ATMOSPHERES ATELEVATED TEMPERATURES WHICH COMPRISES A MOLYBDENUM-BASE PORTION, ANINTERMEDIATE LAYER OF A METAL SELECTED FROM THE GROUP CONSISTING OFIRON, NICKEL, COBALT AND ALLOYS THEREOF COVERING THE EXPOSED SURFACE OFSAID PORTION, SAID INTERMEDIATE LAYER BEING MERGED INTERALLY WITH SAIDMOLYBDENUM-BASE SURFACE AND BEING CHARRACTERIZED BY A DIFFUSION BARRIERZONE CONTAINING MOLYBDENUM, AND A SURFACE LAYER OF METAL SELECTED FROMTHE GROUP CONSISTING OF CHROMIUM, SILICON, ALLUMINUM, ZIRCONIUM ANDALLOYS THEREOF COVERING SAID INTERMEDIATE LAYER AND MERGED THEREWITH,WHEREBY SAID BODY IMPROVED RESISTANCE TO OXIDATION AT ELEVATEDTEMPERATURE OF ABOUT 1650* F. AND HIGHER.